In the field of data transmission by which digital data representing various kinds of signal information are transmitted, there have been proposed to subject digital data which are to be transmitted to enciphering process at a transmission side and to reproduce original data by subjecting the enciphered digital data to deciphering process at a receiving side, in order to prevent the digital data from being eavesdropped on a data transmission line. One of typical algorisms for enciphering digital data is the DES (Date Encryption Standard) published in 1977 by the National Bureau of Standards, the United State of America.
With cipher-transmission based on the DES, digital data are enciphered in accordance with the rules determined by enciphering key data prepared previously to produce enciphered digital data and the enciphered digital data are deciphered in accordance with the rules determined by deciphering key data prepared previously to reproduce original digital data. The deciphering key data are prepared to be the same as the enciphering key data so that each of the deciphering key data and the enciphering key data are formed with common data. The algorisms for enciphering and deciphering have been opened to the public and the common key data are kept secret for the purpose of enciphering.
FIG. 1 shows a basic structure of a cipher-transmission system according to the DES. In the basic structure shown in FIG. 1, digital data to be transmitted are supplied to a DES enciphering portion 11 as original data. Enciphering key data prepared previously are also supplied to the DES enciphering portion 11. In the DES enciphering portion 11, the original data are subjected to the DES enciphering process in accordance with the rules determined by the enciphering key data to produce enciphered data. The enciphered data obtained from the DES enciphering portion 11 are transmitted through a data transmission line 12 having one end thereof connected with the DES enciphering portion 11.
The enciphered data having been transmitted through the data transmission line 12 are supplied to a DES deciphering portion 13 with which the other end of the data transmission line 12 is connected. Deciphering key data which is the same as the enciphering key data are also supplied to the DES deciphering portion 13. In the DES deciphering portion 13, the enciphered data are subjected to the DES deciphering process in accordance with the rules determined by the deciphering key data to reproduce the original data.
In the field of video signals, digitalization of video signals has been aimed for actualizing diversification in information to be transmitted, improvements in quality of images reproduced from the video signal and so on. For example, there has been proposed the High Definition Television (HDTV) system which uses a digital video signal composed of digital word sequence data representing video signal information. The digital video signal under the HDTV system (hereinafter, referred to the HD signal) is formed in accordance with, for example, the BTA S-002 which is one of a series of standards established by the Broadcasting Technology Association (BTA) in Japan so as to be in the form of Y and P.sub.B/P.sub.R signals or G, B and R signals. In the case of the Y and P.sub.B/P.sub.R signals, Y represents a luminance signal and P.sub.B/P.sub.R represent color difference signals. In the case of the G, B and R signals, G, B and R represent green, blue and red primary color signals, respectively.
The HD signal is a digital television signal by which each frame picture is formed with first and second field pictures each appearing at a rate of 60 Hz and which is constituted in accordance with an arrangements including a frame rate of 30 Hz, 1125 lines per frame, 2,200 data samples per line and a sampling frequency of 74.25 MHz. For example, the HD signal in the form of Y and P.sub.B/P.sub.R signals is constituted in accordance with such data formats as shown in FIGS. 2A and 2B.
The data formats shown in FIGS. 2A and 2B include a part of a portion corresponding to a line period (hereinafter, referred to a line period portion) of a luminance signal data sequence (hereinafter, referred to a Y data sequence) as shown in FIG. 2A, which represents a luminance signal component of a video signal, and a part of a line period portion of a color difference signal data sequence (hereinafter, referred a P.sub.B/P.sub.R data sequence) as shown in FIG. 2B, which represents color difference signal components of the video signal. Each of data words constituting the Y data sequence or the P.sub.B/P.sub.R data sequence is composed of 10 bits. This means that each of the Y data sequence and the P.sub.B/P.sub.R data sequence constitutes 10-bit word sequence data having a word transmission rate of, for example, 74.25 Mwps.
In the Y data sequence, each line period portion of which is formed with a portion corresponding to a horizontal blanking period and a portion corresponding to a video data period appearing after the horizontal blanking period, time reference code data SAV (Start of Active Video) which are composed of four 10-bit words (3FF(Y), 000(Y), 000(Y), XYZ(Y): 3FF and 000 are hexadecimal numbers and (Y) indicates a word contained in the Y data sequence) are provided just before the portion corresponding to the video data period and another time reference code data EAV (End of Active Video) which are composed of four 10-bit words (3FF(Y), 000(Y), 000(Y), XYZ(Y)) are provided just after the portion corresponding to the video data period. Similarly, in the P.sub.B/P.sub.R data sequence, each line period portion of which is formed with a portion corresponding to a horizontal blanking period and a portion corresponding to a video data period appearing after the horizontal blanking period, time reference code data SAV which are composed of four 10-bit words (3FF(C), 000(C), 000(C), XYZ(C) (C) indicates a word contained in the P.sub.B/P.sub.R data sequence) are provided just before the portion corresponding to the video data period and another time reference code data EAV which are composed of four 10-bit words (3FF(C), 000(C), 000(C), XYZ(C)) are provided just after the portion corresponding to the video data period. The time reference code data EAV and SAV contained in the Y data sequence are provided in the portion corresponding to the horizontal blanking period of the Y data sequence and the time reference code data EAV and SAV contained in the P.sub.B/P.sub.R data sequence are provided in the portion corresponding to the horizontal blanking period of the P.sub.B/P.sub.R data sequence.
Initial three 10-bit words (3FF, 000,000) of four 10-bit words (3FF, 000,000, XYA), each of which is shown with (Y) or (C), are used for establishing word synchronization or line synchronization and a last one 10-bit word (XYZ) of four 10-bit words (3FF, 000,000, XYA), which is also shown with (Y) or (C), is used for discriminating the first field from the second field in each frame or for discriminating the time reference code data EAV from the time reference code data SAV.
For the HD signal constituted with the Y data sequence and the P.sub.B/P.sub.R data sequence as described above, some forbidden codes, each of which can not be used as an information code forming video data or ancillary data, and which include timing discrimination codes forming the time reference code data SAV or EAV, are predetermined. When each of the Y data sequence and the P.sub.B/P.sub.R data sequence constitutes 10-bit word sequence data, the forbidden codes mentioned above are 000h to 003h and 3FCh to 3FFh (000 to 003 and 3FC to 3FF are hexadecimal numbers and h indicates a hexadecimal number), that is, 0000000000 to 0000000011 and 1111111100 to 1111111111, as shown in FIG. 3.
When the HD signal constituted with the Y data sequence and the P.sub.B/P.sub.R data sequence is subjected to transmission through a data transmission line, it is desired for the HD signal to be converted to serial data from word sequence data so as to be subjected to serial transmission through a simplified data transmission line. In connection with the serial transmission of the HD signal constituted with the Y data sequence and the P.sub.B/P.sub.R data sequence, it has been standardized to transmit the HD signal in conformity with the HD SDI (High Definition Serial Digital Interface) according to the BTA S-004 which is one of a series of standards established by the BTA in Japan.
In the transmission of the HD signal in conformity with the HD SDI, the Y data sequence and the P.sub.B/P.sub.R data sequence are multiplexed, with their portions corresponding to the horizontal blanking periods in each of which the time reference code data EAV and SAV are provided and which synchronize with each other, to produce a multiple word sequence as shown in FIG. 4 and then the multiple word sequence is converted to serial data to be transmitted. Each of data words constituting the multiple word sequence shown in FIG. 4 is composed of 10 bits and the word transmission rate of the multiple word sequence shown in FIG. 4 is set to be 74.25Mwps.times.2=148.5Mwps. In the multiple word sequence thus obtained as shown in FIG. 4, multiple time reference code data (multiple SAV) which are composed of eight 10-bit words (3FF(C), 3FF(Y), 000(C), 000(Y), 000(C), 000(Y), XYZ(C), XYZ(Y)) are provided just before the portion corresponding to a video data period and another multiple time reference code data EAV (multiple EAV) which are composed of eight 10-bit words (3FF(C), 3FF(Y), 000(C), 000(Y), 000(C), 000(Y), XYZ(C), XYZ(Y)) are provided just after the portion corresponding to the video data period.
The each of the 10-bit words constituting the multiple word sequence is sent bit by bit from the least significant bit (LSB) to the most significant bit (MSB) so that the multiple word sequence is converted to a serial data. Then, the serial data is subjected to scrambling process to produce a serial transmission HD signal (hereinafter, referred to an HD-SDI signal) and the HD-SDI signal is transmitted through a data transmission line. The HD-SDI signal thus transmitted has a bit transmission rate of, for example, 148.5Mwps.times.10=1.485 Gbps.
In the case of the transmission of the HD-SDI signal through the data transmission line, it is also desired to subject the HD-SDI signal to enciphering process at a transmission side and to reproduce original HD-SDI data by subjecting the enciphered HD-SDI data to deciphering process at a receiving side, in order to prevent the HD-SDI data from being eavesdropped on the data transmission line. Such cipher-transmission of the HD-SDI signal can be theoretically carried out with a cipher-transmission system which is similar to the cipher-transmission system according to the DES having the basic structure shown in FIG. 1.
For example, when an HD signal is converted to an HD-SDI signal in accordance with the HD SDI to be transmitted through a data transmission line and the transmitted HD-SDI signal is reconverted to the HD signal in accordance with the HD SDI to be supplied to, for example, a video projector which operates to display images based on the HD signal, it is considered to have such a cipher-transmission system as shown in FIG. 5 for conducting the cipher-transmission of the HD-SDI signal.
In the cipher-transmission system shown in FIG. 5, an HD-SDI signal DHS derived from an HD-SDI signal generating portion 15, in which an HD signal obtained from a video camera or the like is converted to the HD-SDI signal HDS in accordance with the HD SDI, is supplied to an HD-SDI enciphering portion 16. Enciphering key data DDK prepared previously are also supplied to the HD-SDI enciphering portion 16. In the HD-SDI enciphering portion 16, the HD-SDI signal DHS is first subjected to serial to parallel (S/P) conversion to reproduce the original HD signal constituted with Y and P.sub.B/P.sub.R data sequences and a video data portion of the reproduced HD signal is subjected to the DES enciphering process in accordance with the rules determined by the enciphering key data DDK to produce an enciphered HD signal. Then, in the HD-SDI enciphering portion 16, the enciphered HD signal is subjected to parallel to serial (P/S) conversion to produce enciphered serial data DHSE. The enciphered serial data DHSE are derived from the HD-SDI enciphering portion 16 to be transmitted through a data transmission line 17 having one end thereof connected with the HD-SDI enciphering portion 16.
The enciphered serial data DHSE having been transmitted through the data transmission line 17 are supplied to an HD-SDI deciphering portion 18 with which the other end of the data transmission line 17 is connected. Deciphering key data DDK which is the same as the enciphering key data DDK supplied to the HD-SDI enciphering portion 16 are also supplied to the HD-SDI deciphering portion 18. In the HD-SDI deciphering portion 18, the enciphered serial data DHSE are subjected to the S/P conversion to reproduce the enciphered HD signal and a video data portion of the enciphered HD signal is subjected to the DES deciphering process in accordance with the rules determined by the deciphering key data DDK to reproduce the original HD signal constituted with Y and P.sub.B/P.sub.R data sequences. Then, in the HD-SDI deciphering portion 18, the Y and P.sub.B/P.sub.R data sequences constituting the reproduced HD signal are multiplexed with each other in accordance with the HD SDI to produce a word multiple data sequence and the word multiple data sequence thus obtained are subjected to the P/S conversion to reproduce the HD-SDI signal DHS.
The HD-SDI signal DHS obtained from the HD-SDI deciphering portion 18 is supplied to a video projector 19. In the video projector 19, the HD signal is reproduced from the HD-SDI signal DHS and used for display of images.
In such a manner as described above, the cipher-transmission of the HD-SDI signal is seemingly carried out. However, in the cipher-transmission system shown in FIG. 5, a serious problem, with which the deciphering process to which the enciphered serial data DHSE are subjected in the HD-SDI deciphering portion 18 is interfered and the reproduction of the HD signal from the HD-SDI signal DHI can not be appropriately carried out in the video projector 19, is brought about.
This problem is explained as follows.
When the HD-SDI signal DHS is converted to the HD signal and the video signal portion of the HD signal is subjected to the DES enciphering process in accordance with the rules determined by the enciphering key data DDK to produce the enciphered HD signal in the HD-SDI enciphering portion 16, the bidden codes aforementioned, that is, 000h to 003h and 3FCh to 3FFh are undesirably contained with a certain probability in the video data portion of the enciphered HD signal though the video data portion of the HD signal does not contain anyone of the forbidden codes of 000h to 003h and 3FCh to 3FFh. As a result, the enciphered serial data DHSE are produced based on the enciphered HD signal which has the video data portion containing the forbidden codes in the HD-SDI enciphering portion 16 and then transmitted from the HD-SDI enciphering portion 16 through the data transmission line 17 to the HD-SDI deciphering portion 18.
The forbidden codes are originally contained in the HD signal in the form of the timing identification codes constituting the time reference codes SAV and EAV and portions of the HD-SDI signal DHS which corresponds to the serial data converted from the forbidden codes constituting the time reference codes data SAV and EAV are detected to be used for making word-synchronization between the HD-SDI signal DHS and the reproduced HD signal so that the reproduced HD signal is properly obtained when the original HD signal is reproduced from the HD-SDI signal DHS.
Under such a situation, when the enciphered serial data DHSE which are produced based on the enciphered HD signal having the video data portion containing the forbidden codes is transmitted from the HD-SDI enciphering portion 16 through the data transmission line 17 to the HD-SDI deciphering portion 18, it is feared in the HD-SDI deciphering portion 18 that a portion of the enciphered serial data DHSE which corresponds to the serial data converted from the forbidden codes contained in video data portion of the enciphered HD signal is undesirably detected, in addition to portions of the enciphered serial data DHSE which properly correspond to the serial data converted from the forbidden codes contained in the HD signal for constituting the time reference codes SAV and EAV, just as a portion of the enciphered serial data DHSE which corresponds to the serial data converted from the forbidden codes constituting the time reference codes data SAV or EAV. If the portion of the enciphered serial data DHSE which corresponds to the serial data converted from the forbidden codes contained in video data portion of the enciphered HD signal is also detected just as the portion of the enciphered serial data DHSE which corresponds to the serial data converted from the forbidden codes constituting the time reference codes data SAV or EAV when the ciphered HD signal is reproduced from the enciphered serial data DHSE in the HD-SDI deciphering portion 18, appropriate word-synchronization between the enciphered serial data DHSE and the ciphered HD signal to be reproduced is not made and therefore the ciphered HD signal can not be properly reproduced.
Further, as a result, the HD-SDI signal DHS which is obtained from the HD-SDI deciphering portion 18 to be supplied to the video projector 19 comes to have improper contents and accordingly the HD signal which is reproduced from the HD-SDI signal DHS from the HD-SDI deciphering portion 18 in the video projector 19 also comes to have improper video data.
The problems mentioned above are brought about by the data transmission in which the forbidden codes are undesirably contained with a certain probability in the video data portion of the enciphered HD signal and thereby the ciphered serial data DHSE contain an undesirable portion thereof corresponding to the serial data converted from the forbidden codes when the HD-SDI signal DHS is reconverted to the HD signal to be subjected to the DES enciphering process in accordance with the rules determined by the deciphering key data DDK to produce the ciphered HD signal and the ciphered serial data DHSE are obtained based on the ciphered HD signal to be transmitted in the HD-SDI enciphering portion 16.
Accordingly, it is an object of the present invention to provide a first method of transmitting data which can be applicable to enciphered data transmission in which digital information data which correspond to serial data obtained based on word sequence data which contain digital information data in which forbidden codes including timing identification codes are contained and time reference code data constituted with the timing identification codes, for example, such data as constituting an HD-SDI signal, are subjected to enciphering process to produce enciphered serial data and the enciphered serial data are transmitted, and by which the ciphered data transmission is carried out under a condition wherein the enciphered serial data can be prevented from containing an undesirable portion thereof corresponding to serial data converted from the forbidden codes.
Another object of the present invention is to provide a first apparatus for transmitting data in which the first method of transmitting data mentioned above is carried out.
A further object of the present invention is to provide a second method of transmitting data which can be applicable to enciphered data transmission in which digital information data which correspond to serial data obtained based on word sequence data which contain digital information data in which forbidden codes including timing identification codes are contained and time reference code data constituted with the timing identification codes, for example, such data as constituting an HD-SDI signal, are subjected to enciphering process to produce enciphered serial data and the enciphered serial data are transmitted, and by which the ciphered data transmission is carried out under a condition wherein the enciphered serial data can be prevented from containing an undesirable portion thereof corresponding to serial data converted from the forbidden codes and the original digital information data can be surely reproduced by subjecting enciphered digital information data obtained based on the transmitted enciphered serial data to deciphering process.
A still further object of the present invention is to provide a second apparatus for transmitting data in which the second method of transmitting data mentioned above is carried out.